Piper Navajo PA-31 Service Manual page 730

PIPER NAVAJO SERVICE MANUAL
11-40. CHECKING ALTERNATOR PARALLELING SYSTEM. The alternator paralleling
system incorporates an ammeter which provides for an independent check of each
alternator, as well as the charge/discharge current of the battery. In the event either
ALTERNATOR INOPERATIVE light begins to glow or the ammeter check for either
alternator fails to indicate an output, check the appropriate alternator circuit breaker
switch, also the voltage regulator circuit breaker. If the circuit breakers are in their normal
operating position a further check of the alternator system should be accomplished. (Refer
to Figure 11-31.)
a. Verify that the ammeters are operating properly.
b. Disconnect the output (+) lead at the alternator.
c. Disconnect the field F-2 lead at the alternator.
CAUTION
DO NOT ALLOW THE FIELD LEAD TO COME IN
CONTACT WITH AIRFRAME GROUND WHEN THE
MASTER
SWITCH IS
ON AS THE
VOLTAGE
REGULATOR WILL BE DAMAGED.
d. Verify that all electrical units are off and the battery is fully charged.
e. Turn ON the section of the master switch for the alternator being tested. (L or R.)
f. To check the alternator output circuit, connect a voltmeter or 24-volt test light to
the previously disconnected output (+) lead. Check that the circuit breaker switch for the
alternator under test is turned on. If a reading of approximately 24-volts is obtained on the
voltmeter, or the test light glows, the output circuit is operational.
g. Should there be no indication of voltage, trace back through the output circuit until
voltage is indicated. (Refer to Figure 11-31.) A component that does not indicate voltage
at both its input and output terminals should be replaced.
h. Check the field circuit by connecting a voltmeter to previously disconnected field
(F-2) lead. If a reading of approximately 1 to 3-volts is obtained on the voltmeter, the field
circuit is operative.
i. If voltage is present at both the output and field leads, the alternator should be
checked for a possible malfunction. (Refer to Paragraph 11-29.)
11-41. REGULATOR.
11-42. REGULATOR COMPONENTS (PRESTOLITE). Alternator output voltage can,
within the limits of the design capability of the alternator, be controlled by properly varying
the average level of current flow in the rotor winding and the PRESTOLITE full electronic
.solid state regulator is well suited for this purpose. The PRESTOLITE alternator, due to its
design, has self-limiting current characteristics and needs no current-limiting unit in the
regulator.
a. Transistor: The transistor is an electronic switch which can turn on and turn off the
flow of current in an electric circuit. It has no mechanical or moving parts to wear out.
Reissued: 10/12/79
ELECTRICAL SYSTEM
4C4